Aqueous Al(III) Speciation by High-Performance Cation Exchange Chromatography with Fluorescence Detection of the Aluminum-Lumogallion Complex

Abstract

Soluble complexes of aluminum, including fluorides, citrates, acetates, and silicate, were separated from uncomplexed Al and quantitated using gradient elution cation exchange HPLC. Fluorescence detection of the Al-lumogallion complex allowed detection as low as 7 nM with linearity to 58 {mu}M and relative standard deviations of 3% at the 2 {mu}M level. Dissociation of the complexes on the column and inadequate detection of Al organic complexes, problems in previous methods, were not observed. Species concentrations at various pH and ionic strengths agreed well with equilibrium speciation calculations for solutions of aluminum citrates and aluminum fluorides. The formation constants were determined for AlOSiO{sub 3}H{sub 3}{sup 2+}, an aluminum species considered in the modeling of acid-impacted aquatic systems, and for AlCit-(-H){sup -}, a species predominant in basic solutions. Formation constants were also estimated for two aluminum acetate complexes, AlOAc{sup 2-} and AlOHOAc{sup +}, the identification of the latter being previously unconfirmed. 46 refs., 5 figs., 1 tab.